Preceding vehicle selection apparatus

ABSTRACT

A preceding vehicle selection apparatus estimates a curvature of a road on which an own vehicle is traveling, detects an object ahead of the own vehicle, and determines a relative position in relation to the own vehicle. Based on the curvature and the relative position, an own vehicle lane probability instantaneous value is determined. This instantaneous value is a probability of the object ahead being present in the same vehicle lane as the own vehicle. By a filter calculation on the instantaneous value, an own vehicle lane probability is determined. Based on the own vehicle lane probability, a preceding vehicle is selected. An inter-vehicle time required for the own vehicle to reach a detection position of the object ahead is calculated. Based on the inter-vehicle time, characteristics of the filter calculation are changed such that an effect of the own vehicle lane instantaneous value increases as the inter-vehicle time decreases.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromJapanese Patent Application No. 2013-204473, filed Sep. 30, 2013, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Technical Field

The present invention relates to a technology for selecting a vehicle(preceding vehicle) that is traveling ahead of an own vehicle.

Related Art

As a technology for reducing operating load placed on a driver who isdriving a vehicle, an inter-vehicle control apparatus is known. Theinter-vehicle control apparatus detects a vehicle (preceding vehicle)that is traveling ahead of the own vehicle. The inter-vehicle controlapparatus controls the vehicle speed and the like to maintain a certaindistance between the own vehicle and the preceding vehicle, enabling theown vehicle to automatically track the preceding vehicle.

In this type of apparatus, an estimated curve radius of the road onwhich the own vehicle is traveling is determined based on the yaw rateand vehicle speed of the own vehicle. In addition, a radar apparatus orthe like is used to detect the position of the vehicle that is presentahead of the own vehicle. Based on the estimated curve radius and theposition of the preceding vehicle, an own vehicle lane probability isdetermined for each detected preceding vehicle. The own vehicle laneprobability indicates the probability of the vehicle being present inthe same lane as the estimated traveling road of the own vehicle.Selection of a preceding vehicle and cancellation of the selection areperformed based on the own vehicle lane probability.

However, because the detection values of the yaw rate vary, thecalculation results for the estimated curve radius also vary. Therefore,to suppress the effects caused by the variation, a filter calculation isperformed on the own vehicle lane probability.

Furthermore, at close distances, it is preferable that the filter beweak to ensure responsiveness, so that responses can be quickly maderegarding merging vehicles and the like. However, at long distances,error in the estimated traveling road determined based on the estimatedcurve radius increases. When the value of the own vehicle laneprobability significantly changes in accompaniment, a phenomenon occursin which the preceding vehicle is frequently set and canceled.Therefore, it is preferable that the filter be strong to ensurestability of the own vehicle lane probability. As a result, a filtercoefficient is also changed depending on the inter-vehicle distance(refer to, for example, JP-B-3427815).

However, whether the driver senses the inter-vehicle distance to be longor short differs depending on the vehicle speed. Therefore, in theconventional method of changing the filter characteristics based on theinter-vehicle distance, a problem occurs in that suitable filtercharacteristics cannot be actualized at every vehicle speed.

In other words, when the filter is set so as to become stronger near theinter-vehicle distance of 80 m, this setting is suited to the senses ofthe driver during low-speed cruising. However, the timing at which thefilter strengthens is too early during high-speed cruising. Therefore,the driver senses that detection of a merging vehicle, for whichresponsiveness is required, becomes slow during high-speed cruising.

SUMMARY

It is thus desired to provide a technology in which a preceding vehicleis selected at a timing suited to the senses of a driver, regardless ofvehicle speed.

An exemplary embodiment provides a preceding vehicle selection apparatusthat includes curvature estimating means, object position detectingmeans, instantaneous probability calculating means, filter calculatingmeans, preceding vehicle selecting means, inter-vehicle time calculatingmeans, and filter characteristics setting means.

The curvature estimating means estimates a curvature of a traveling roadon which the own vehicle is traveling. The object position detectingmeans detects an object ahead. The object ahead is an object presentahead of the own vehicle. The object position detecting means determinesa relative position in relation to the own vehicle, for each objectahead. The instantaneous probability calculating means repeatedlydetermines an own vehicle lane probability instantaneous value for eachobject ahead, based on the estimated curvature estimated by thecurvature estimating means and the relative position determined by theobject position detecting means. The own vehicle lane probabilityinstantaneous value is an instantaneous value of a probability of theobject ahead being present in the same vehicle lane as the own vehicle.The filter calculating means determines an own vehicle lane probabilityby performing a filter calculation on the own vehicle lane probabilityinstantaneous value calculated by the instantaneous probabilitycalculating means. The preceding vehicle selecting means selects apreceding vehicle based on the own vehicle lane probability determinedby the filter calculating means.

The inter-vehicle time calculating means calculates an inter-vehicletime for each object ahead. The inter-vehicle time indicates a timerequired for the own vehicle to reach a detected position of the objectahead. The filter characteristics setting means changes characteristicsof filter calculation such that an effect of the own vehicle laneinstantaneous value increases as the inter-vehicle time decreases, basedon the inter-vehicle time determined by the inter-vehicle timecalculating means.

In the preceding vehicle selection apparatus of the present inventionconfigured as described above, the characteristics of filter calculationchange based on the inter-vehicle time. Therefore, filter calculationthat takes into consideration various characteristics (such as thecharacteristic of an estimated curve radius) that change depending onthe own vehicle speed can be actualized. As a result, the precedingvehicle can be selected at the timing suited to the senses of the driverat all vehicle speeds (in other words, regardless of the vehicle speed).

In addition, the present invention can be actualized by variousembodiments in addition to the above-described preceding vehicleselection apparatus. For example, the present invention can beactualized by a system of which the preceding vehicle selectionapparatus is a constituent element, or a program enabling a computer tofunction as each means configuring the preceding vehicle selectionapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing an overall configuration of aninter-vehicle control system including an inter-vehicle controller thatis applicable to a preceding vehicle selection apparatus according to anembodiment;

FIG. 2 is a flowchart of a preceding vehicle selection process performedby the inter-vehicle controller shown in FIG. 1;

FIG. 3 is a graph showing details of a filter constant table that isused to calculate a filter constant from an inter-vehicle time at stepS160 shown in FIG. 2;

FIG. 4 is a graph showing changes in an own vehicle lane probabilitybefore and after a filter process performed by the inter-vehiclecontroller shown in FIG. 1;

FIG. 5 is an explanatory diagram effects achieved by the filter constantbeing changed depending on the inter-vehicle time in the embodiment; and

FIG. 6 is a block diagram showing a functional configuration of theinter-vehicle controller shown in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

An embodiment to which the present invention is applied will hereinafterbe described with reference to the drawings.

As shown in FIG. 1, an inter-vehicle control system 1 is mounted in anautomobile. The inter-vehicle control system 1 controls the vehiclespeed to maintain the inter-vehicle distance to a vehicle (precedingvehicle) traveling ahead of the own vehicle at a suitable distance.

The inter-vehicle control system 1 is mainly configured by aninter-vehicle controller 4 that works as a preceding vehicle selectionapparatus according to the embodiment. The inter-vehicle control system1 also includes a sensor group 2, a switch group 3, and an electroniccontrol unit (ECU) group 5. The sensor group 2 is composed of varioussensors used to detect the situation surrounding the vehicle, as well asthe behavior and state of the vehicle. The switch group 3 is composed ofvarious switches used to input instructions to the inter-vehiclecontroller 4. The ECU group 5 performs various control operations basedon commands from the inter-vehicle controller 4.

The sensor group 2 includes at least a radar sensor 21, a yaw ratesensor 22, a wheel speed sensor 23, and a steering sensor 24.

The radar sensor 21 outputs laser light towards the area ahead of theown vehicle so as to scan a predetermined angle range. The radar sensor21 also detects reflected light of the laser light. The radar sensor 21determines the distance to an object that has reflected the laser lightbased on the amount of time required for the laser light to reach andreturn from the object. In addition, the radar sensor 21 determines thedirection in which the object is present based on the direction in whichthe laser light is irradiated when the reflected light is detected. Theradar sensor 21 is not limited that which uses laser light. The radarsensor 21 may use millimeter waveband or micro-millimeter waveband radiowaves, ultrasonic waves, or the like.

The yaw rate sensor 22 outputs signals based on the yaw rate of thevehicle.

The wheel speed sensor 23 is attached to each of the left front wheel,the right front wheel, the left rear wheel, and the right rear wheel.Each wheel speed sensor 23 outputs a pulse signal having an edge (pulseedge) that is formed at every predetermined angle depending on therotation of the wheel shaft. In other words, the wheel speed sensor 23outputs a pulse signal having a pulse interval based on the rotationspeed of the wheel shaft.

The steering sensor 24 outputs signals based on a relative steeringangle of the steering wheel (amount of change in the steering angle) oran absolute steering angle of the steering wheel (actual steering anglewith reference to the steering position when the vehicle travelingstraight ahead).

The switch group 3 includes at least a control permission switch 31 anda control mode selection switch 32.

The control permission switch 31 is used to input whether or notexecution of adaptive cruise control (ACC) is permitted. ACC is a knowncontrol operation that enables the vehicle to travel at a predeterminedset speed when a preceding vehicle is not present. ACC performs trackingcruise in which a predetermined inter-vehicle distance is maintainedwhen a preceding vehicle is present.

The control mode selection switch 32 is used to select ACC control mode.

The ECU group 5 includes at least an engine ECU 51, a brake ECU 52, anda meter ECU 53.

The engine ECU 51 controls engine start/stop, fuel injection amount,ignition timing, and the like. The engine ECU 51 includes a centralprocessing unit (CPU), a read-only memory (ROM), a random access memory(RAM), and the like. Specifically, the engine ECU 51 controls a throttleACT based on detection values from a sensor that detects the depressionamount of an accelerator pedal. The throttle ACT is an actuator thatopens and closes a throttle provided in an air intake pipe. In addition,the engine ECU 51 controls the throttle ACT to increase and decrease thedriving force of an internal combustion engine based on instructionsfrom the inter-vehicle controller 4.

The brake ECU 52 controls braking of the own vehicle. The brake ECU 52includes a CPU, a ROM, a RAM, and the like. Specifically, the brake ECU52 controls a brake ACT based on detection values from a sensor thatdetects the depression amount of a brake pedal. The brake ACT is anactuator that opens and closes a pressure-increase regulating valve anda pressure-decrease regulating valve provided in a hydraulic brakecircuit. In addition, the brake ECU 52 controls the brake ACT toincrease and decrease braking force of the own vehicle based oninstructions from the inter-vehicle controller 4.

The meter ECU 53 performs is display control of a meter display that isprovided in the vehicle, based on instructions from each unit of thevehicle including the inter-vehicle controller 4. The meter ECU 53includes a CPU, a ROM, a RAM, and the like. Specifically, the meter ECU53 displays, in the meter display, vehicle speed, engine rotation speed,and the execution state and control mode of control performed by theinter-vehicle controller 4.

The inter-vehicle controller 4 is mainly configured by a knownmicrocomputer that includes a CPU, a ROM, a RAM, and the like. Inaddition, the inter-vehicle controller 4 includes a detection circuit,an analog/digital (A/D) conversion circuit, an input/output (I/O)interface, a communication circuit, and the like. The detection circuitand the A/D conversion circuit detect signals outputted from the sensorgroup 2 and convert the signals to digital values. The I/O interfacereceives input from the switch group 3. The communication circuitcommunicates with the ECU group 5. These hardware configurations arecommon. Therefore, detailed descriptions thereof are omitted.

In the inter-vehicle controller 4, the CPU executes one or more programsstored in advance in the memory (e.g., ROM) to perform a predeterminedpreceding vehicle determination process as described in detail below.Thus, as shown in FIG. 6, the inter-vehicle controller 4 is capable ofworking as the preceding vehicle selection apparatus that includes acurvature estimating unit 41 (equivalent to curvature estimating means),an object position detecting unit 42 (equivalent to object positiondetecting means), an instantaneous probability calculating unit 43(equivalent to instantaneous probability calculating means), a filtercalculating unit 44 (equivalent to filter calculating means), apreceding vehicle selecting unit 45 (equivalent to preceding vehicleselecting means), an inter-vehicle time calculating unit 46 (equivalentto inter-vehicle time calculating means), and a filter characteristicssetting unit 47 (equivalent to filter characteristics setting means).

When ACC is permitted by the control permission switch 31, theinter-vehicle controller 4 periodically (such as every 100 ms) performsa preceding vehicle determination process. In addition, theinter-vehicle controller 4 performs an inter-vehicle control processselected by the control mode selection switch 32 using the determinationresult of the preceding vehicle determination process.

Of the processes, in the inter-vehicle control process, theinter-vehicle controller 4 ordinarily controls the vehicle speed byoutputting instructions to increase and decrease the acceleratoroperation amount to the engine ECU 51. When control cannot be supportedusing the accelerator operation amount, the inter-vehicle controller 4restricts the vehicle speed by outputting a brake command to the brakeECU 52. In addition, the inter-vehicle controller 4 outputs, to themeter ECU 53, various pieces of ACC-related display information andcommands for generating an alert when predetermined conditions are met.

Here, details of the preceding vehicle determination process performedby the inter-vehicle controller 4 will be described with reference tothe flowchart shown in FIG. 2. In the embodiment, a program that enablesthe CPU of the inter-vehicle controller 4 to perform the precedingvehicle determination process shown in FIG. 2 is stored in the memory(e.g., ROM) of the inter-vehicle controller 4 in advance.

When the preceding vehicle determination process is started, first, atstep S110, the inter-vehicle controller 4 loads the distance and anglemeasurement data detected by the radar sensor 21.

At subsequent step S120, the inter-vehicle controller 4 converts theloaded distance and angle measurement data, from the polar coordinatesystem expressed by the data to an orthogonal coordinate system. Basedon the converted data, the inter-vehicle controller 4 performs an objectrecognition process to recognize an object that is present ahead of theown vehicle. In the object recognition process, the inter-vehiclecontroller 4 clusters the distance and angle measurement data. Theinter-vehicle controller 4 then determines the center positioncoordinates of the object, the relative speed to the own vehicle, andthe like for each cluster. The object recognized herein is referred to,hereinafter, as a “target”. The inter-vehicle controller 4 performs theprocessing operation at step S120, and then is capable of working as theobject position detecting unit 42 in FIG. 6.

At subsequent step S130, based on the yaw rate γ detected by the yawrate sensor 22 and the own vehicle speed V calculated based on thedetection results from the wheel speed sensors 23, an estimated R iscalculated based on the following expression (1). The estimated R is thecurve radius (reciprocal of the curvature) of an own vehicle travelingcurve. The inter-vehicle controller 4 performs the processing operationat step S130, and then is capable of working as the curvature estimatingunit 41 in FIG. 6.

$\begin{matrix}{R = \frac{V}{\gamma}} & (1)\end{matrix}$

At subsequent step S140, the inter-vehicle controller 4 calculates anown vehicle lane probability instantaneous value of the objectrecognized at step S120. The own vehicle lane probability is a parameterindicating the likelihood of the target being a vehicle that istraveling in the same lane as the own vehicle. The own vehicle laneprobability instantaneous value is an instantaneous value of the ownvehicle lane probability calculated based on detection data in thecurrent processing cycle.

In this process, first, the inter-vehicle controller 4 determines thepositions of all targets obtained at step S120 (object recognitionprocess) as positions converted under a premise that the traveling roadon which the own vehicle is traveling is a straight road. Theinter-vehicle controller 4 uses the estimated R calculated at step S130to determine the positions of all targets. Then, for each target, theinter-vehicle controller 4 determines the own vehicle lane probabilityinstantaneous value from the converted position of the target using anown vehicle lane probability map that is set in advance.

The own vehicle lane probability map is a known map in which theprobability tends to be the highest when the converted position is nearthe front of the own vehicle and at a close distance. In addition, theprobability tends to decrease as the converted position becomes fartherand shifted in the lateral direction from the front of the own vehicle.A specific example and usage of the own vehicle lane probability map aredescribed in detail in JP-B-3427815 and the like. A reason forexpressing whether or not the target is in the own vehicle lane in termsof probability is that an error is present between the curve radius ofcurvature (estimated R) determined from the yaw rate and the actualcurve radius of curvature. The inter-vehicle controller 4 performs theprocessing operation at step S140, and then is capable of working as theinstantaneous probability calculating unit 43 in FIG. 6.

At subsequent step S150, the inter-vehicle controller 4 calculates aninter-vehicle time for each target. The inter-vehicle time can bedetermined by dividing the distance to the target by the own vehiclespeed. The inter-vehicle controller 4 performs the processing operationat step S150, and then is capable of working as the inter-vehicle timecalculating unit 46 in FIG. 6.

At subsequent step S160, the inter-vehicle controller 4 determines afilter constant α from the inter-vehicle time for each target. Theinter-vehicle controller 4 uses a filter constant table that is set inadvance to determine the filter constant. As shown in FIG. 3, the filterconstant table is set so that the filter constant is an upper limitvalue when the inter-vehicle time is less than a close distancethreshold Ta. The filter constant is a lower limit value when theinter-vehicle time is greater than a long distance threshold Tb. Whenthe inter-vehicle time is the close distance threshold Ta or greater andthe long distance threshold Tb or less, the filter constant is set todecrease from the upper limit value to the lower limit value inproportion with the increase in inter-vehicle time. The inter-vehiclecontroller 4 performs the processing operation at step S160, and then iscapable of working as the filter characteristics setting unit 47 in FIG.6.

At subsequent step S170, the inter-vehicle controller 4 uses thedetermined filter constant α and performs a filter process using thefollowing expression (2) for each processing cycle. In other words, theinter-vehicle controller 4 calculates a weighted average value using aweight that is the filter constant α. The inter-vehicle controller 4thereby calculates the own vehicle lane probability used fordetermination of the preceding vehicle.

Here, the own vehicle lane probability to be determined in a presentprocessing cycle is represented by P(t) (i.e., a present value of theown vehicle lane probability). The own vehicle lane probabilitydetermined in a previous processing cycle is represented by P(t−1)(i.e., a previous value of the own vehicle lane probability). The ownvehicle lane probability instantaneous value determined at step S140 isrepresented by Pc.

$\begin{matrix}{{P(t)} = {{{Pc} \times \frac{\alpha}{100}} + {{P\left( {t - 1} \right)} \times \left( {1 - \frac{\alpha}{100}} \right)}}} & (2)\end{matrix}$

In other words, the filter process works as a so-called low pass filter.As α increases, or in other words, as the inter-vehicle time decreases,the filter becomes weaker (favorable responsiveness). The own vehiclelane probability instantaneous value Pc is more easily reflected in theown vehicle lane probability P(t). As α decreases, or in other words, asthe inter-vehicle time increases, the filter becomes stronger (highstability). The own vehicle lane probability instantaneous value Pc isless easily reflected in the own vehicle lane probability P(t). Theinter-vehicle controller 4 performs the processing operation at stepS170, and then is capable of working as the filter calculating unit 44in FIG. 6.

At subsequent step S180, the inter-vehicle controller 4 determines thepreceding vehicle based on the own vehicle lane probability P(t)calculated at step S170. The inter-vehicle controller 4 then ends theprocess. Specifically, for example, the inter-vehicle controller 4determines a target having the shortest distance to the own vehicle,among the targets of which the own vehicle lane probability P(t) is athreshold (such as 50%) or higher, as the preceding vehicle.

The inter-vehicle controller 4 performs the inter-vehicle controlprocess based on the distance to the target determined to be thepreceding vehicle by the preceding vehicle determination process, andthe relative speed of the target. The inter-vehicle controller 4 outputsvarious commands to the ECU group 5. The inter-vehicle controller 4performs the processing operation at step S180, and then is capable ofworking as the preceding vehicle selecting unit 45 in FIG. 6.

As described above, in the inter-vehicle control system 1, filtercalculation is performed on the own vehicle lane probabilityinstantaneous value Pc when the own vehicle lane probability P(t) iscalculated. The own vehicle lane probability P(t) is used for precedingvehicle determination. Therefore, as shown in FIG. 4, variations in theown vehicle lane probability P(t) are suppressed in comparison to theown vehicle lane probability instantaneous value Pc. As a result,frequent changing of the determination results of the preceding vehicledetermination can be prevented.

In addition, the filter characteristics are changed depending on theinter-vehicle time. The filter becomes stronger when the inter-vehicletime increases. The filter becomes weaker when the inter-vehicle timedecreases. Therefore, for long distances in which the own vehicle laneprobability tends to become unstable, the own vehicle lane probabilityis stabilized. As a result, stable selection of the preceding vehiclecan be actualized. For close distances in which the own vehicle laneprobability is relatively stable, favorably responsive selection of thepreceding vehicle can be actualized.

As shown in FIG. 4, variations in the value of the own vehicle laneprobability P(t) after the filter calculation are actually suppressed incomparison to the own vehicle lane probability instantaneous value Pcbefore the filter calculation. As a result, it is clear that frequentchanging of the determination result of the preceding vehicledetermination is suppressed.

In addition, in the inter-vehicle control system 1, the filtercharacteristics are changed based on the inter-vehicle time. Therefore,unlike when the filter characteristics are changed based on theinter-vehicle distance, the preceding vehicle can be selected at atiming suited to the senses of the driver, at all vehicle speeds (inother words, regardless of the vehicle speed). Inter-vehicle controlusing the preceding vehicle that has been selected at the suitabletimings can be actualized at favorable timings.

In other words, as the own vehicle speed increases, the inter-vehicledistance to the preceding vehicle that feels dangerous becomes shorter.Therefore, in conventional apparatuses that change the filter based onthe inter-vehicle distance, when the filter is set to suit the senses ofthe driver at low speeds, the driver may sense that the timing fordetermining a merging vehicle to be a preceding vehicle is slow (controlresponsiveness is poor) at high speeds. Conversely, as shown in FIG. 5,in the inter-vehicle control system 1 in which the filter is changedbased on the inter-vehicle time, the distance at which the filterweakens (responsiveness of the determination becomes favorable) changesbased on the vehicle speed. Therefore, determination at the timingsuited to the driver can be actualized regardless of the vehicle speed.

Other Embodiments

An embodiment of the present invention is described above. However, thepresent invention is not limited to the above-described embodiment. Itgoes without saying that various embodiments are possible.

(1) According to the above-described embodiment, the estimated R iscalculated from the yaw rate detected by the yaw rate sensor. However,the estimated R may be calculated from the steering angle detected bythe steering sensor.

(2) According to the above-described embodiment, an example is given inwhich the present invention is applied to an inter-vehicle controlsystem. However, this is not limited thereto. The present invention maybe applied to any system as long as the system sets a preceding vehicleand performs control of some kind based on the state of the precedingvehicle or the relative state between the preceding vehicle and the ownvehicle.

(3) The constituent elements of the present invention are conceptual andare not limited to those according to the present embodiment. Forexample, functions provided by a single constituent element may bedispersed among a plurality of constituent elements. Alternatively, thefunctions of a plurality of constituent elements may be integrated in asingle constituent element. In addition, at least some of theconfigurations according to the above-described embodiment may bereplaced with a known configuration having similar functions. Inaddition, at least some of the configurations according to theabove-described embodiment may, for example, be added to or substitutedfor other configurations according to the above-described embodiment.

What is claimed is:
 1. A preceding vehicle selection apparatuscomprising: curvature estimating means that estimates a curvature of atraveling road on which an own vehicle is traveling; object positiondetecting means that detects an object ahead of the own vehicle, anddetermines a relative position in relation to the own vehicle, for eachobject ahead; instantaneous probability calculating means thatrepeatedly determines an own vehicle lane probability instantaneousvalue for each object ahead, based on the estimated curvature estimatedby the curvature estimating means and the relative position determinedby the object position detecting means, the own vehicle lane probabilityinstantaneous value being an instantaneous value of a probability of theobject ahead being present in the same vehicle lane as the own vehicle;filter calculating means that determines an own vehicle lane probabilityby performing a filter calculation on the own vehicle lane probabilityinstantaneous value calculated by the instantaneous probabilitycalculating means; preceding vehicle selecting means that selects apreceding vehicle based on the own vehicle lane probability determinedby the filter calculating means; inter-vehicle time calculating meansthat calculates an inter-vehicle time for each object ahead, theinter-vehicle time indicating a time required for the own vehicle toreach a detected position of the object ahead; and filtercharacteristics setting means that changes characteristics of the filtercalculation such that an effect of the own vehicle lane instantaneousvalue increases as the inter-vehicle time decreases, based on theinter-vehicle time determined by the inter-vehicle time calculatingmeans, wherein: the filter calculating means determines a present valueof the own vehicle lane probability in a present processing cycle byperforming the filter calculation to calculate, using a weight, aweighted average of (i) the own vehicle lane probability instantaneousvalue and (ii) a previous value of the own vehicle lane probabilitydetermined in a previous processing cycle by the filter calculatingmeans, and changes the weight for calculating the weighted average basedon the inter-vehicle time; and the own vehicle lane probability isdetermined by${P(t)} = {{{Pc} \times \frac{\alpha}{100}} + {{P\left( {t - 1} \right)} \times \left( {1 - \frac{\alpha}{100}} \right)}}$where: P(t) is the present value of the own vehicle lane probabilitythat is determined in a present processing cycle; P(t−1) is the previousvalue of the own vehicle lane probability that is determined in aprevious processing cycle; Pc is the own vehicle lane probabilityinstantaneous value; and α is a filter constant that is the weight forcalculating the weighted average.
 2. The preceding vehicle selectionapparatus according to claim 1, wherein: the filter constant is set toan upper limit value when the inter-vehicle time is less than apredetermined first threshold for a close distance; the filter constantis set to a lower limit value when the inter-vehicle time is greaterthan a predetermined second threshold for a long distance; and thefilter constant is set to decrease from the upper limit value to thelower limit value in proportion with an increase in the inter-vehicletime, when the inter-vehicle time is the first threshold or greater andthe second threshold or less.
 3. The preceding vehicle selectionapparatus according to claim 2, wherein the curvature of the travelingroad is estimated by $R = \frac{V}{\gamma}$ where: R is a curve radiusthat is a reciprocal of the curvature of the traveling road; V is aspeed of the own vehicle; and γ is a yaw rate of the own vehicle.
 4. Apreceding vehicle selection method comprising: estimating a curvature ofa traveling road on which an own vehicle is traveling; detecting anobject present ahead of the own vehicle, and determining a relativeposition in relation to the own vehicle, for each object ahead;repeatedly determining an own vehicle lane probability instantaneousvalue for each object ahead, based on the estimated curvature and thedetermined relative position, the own vehicle lane probabilityinstantaneous value being an instantaneous value of a probability of theobject ahead being present in the same vehicle lane as the own vehicle;determining an own vehicle lane probability by performing a filtercalculation on the calculated own vehicle lane probability instantaneousvalue; selecting a preceding vehicle based on the determined own vehiclelane probability; calculating an inter-vehicle time for each objectahead, the inter-vehicle time indicating a time required for the ownvehicle to reach a detected position of the object ahead; and changingcharacteristics of the filter calculation such that an effect of the ownvehicle lane instantaneous value increases as the inter-vehicle timedecreases, based on the determined inter-vehicle time, wherein a presentvalue of the own vehicle lane probability in a present processing cycleis determined by performing the filter calculation to calculate, using aweight, a weighted average of (i) the own vehicle lane probabilityinstantaneous value and (ii) a previous value of the own vehicle laneprobability that is determined in a previous processing cycle; theweight for calculating the weighted average is changed based on theinter-vehicle time; and the own vehicle lane probability is determinedby${P(t)} = {{{Pc} \times \frac{\alpha}{100}} + {{P\left( {t - 1} \right)} \times \left( {1 - \frac{\alpha}{100}} \right)}}$where: P(t) is the present value of the own vehicle lane probabilitythat is determined in a present processing cycle; P(t−1) is the previousvalue of the own vehicle lane probability that is determined in aprevious processing cycle; Pc is the own vehicle lane probabilityinstantaneous value; and α is a filter constant that is the weight forcalculating the weighted average.
 5. The preceding vehicle selectionmethod according to claim 4, wherein: the filter constant is set to anupper limit value when the inter-vehicle time is less than apredetermined first threshold for a close distance; the filter constantis set to a lower limit value when the inter-vehicle time is greaterthan a predetermined second threshold for a long distance; and thefilter constant is set to decrease from the upper limit value to thelower limit value in proportion with an increase in the inter-vehicletime, when the inter-vehicle time is the first threshold or greater andthe second threshold or less.
 6. The preceding vehicle selection methodaccording to claim 5, wherein the curvature of the traveling road isestimated by $R = \frac{V}{\gamma}$ where: R is a curve radius that is areciprocal of the curvature of the traveling road; V is a speed of theown vehicle; and γ is a yaw rate of the own vehicle.